title: Net acid transport by isolated perfused inner medullary collecting ducts.
abstract: The isolated perfused tubule technique was used to study net acid transport in rat terminal inner medullary collecting duct (IMCD) segments. The stop-flow luminal pH [measured fluorometrically with the acidic form of the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein in the lumen] fell 0.35 units below the bath pH in tubules from control rats and 0.53 units below the bath in tubules from deoxycorticosterone-treated rats. Tubules from control rats absorbed bicarbonate and secreted ammonium against concentration gradients, although at low rates. In control rats, 10(-8) M vasopressin added to the bath increased bicarbonate absorption almost threefold. Treatment of rats in vivo with deoxycorticosterone significantly increased the rate of bicarbonate absorption in vitro. In vivo NH4Cl loading also significantly increased bicarbonate absorption. Staining microdissected tubules with acridine orange confirmed that the perfused segments lacked intercalated cells. We conclude that the terminal IMCD spontaneously acidifies the lumen despite an absence of intercalated cells. Bicarbonate absorption appears to be regulated by the same factors that affect net acidification in other collecting duct segments.
authors.affiliation: Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: S M
authors.initials: SM
authors.lastname: Wall
authors.forename: J M
authors.initials: JM
authors.lastname: Sands
authors.forename: M F
authors.initials: MF
authors.lastname: Flessner
authors.forename: H
authors.initials: H
authors.lastname: Nonoguchi
authors.forename: K R
authors.initials: KR
authors.lastname: Spring
authors.forename: M A
authors.initials: MA
authors.lastname: Knepper
mesh_terms: D000042:Absorption; D000143:Acids / Q000378:metabolism*; D000641:Ammonia / Q000378:metabolism; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001692:Biological Transport; D001826:Body Fluids / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D003900:Desoxycorticosterone / Q000031:analogs & derivatives / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007679:Kidney Medulla; D007684:Kidney Tubules / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains; D014667:Vasopressins / Q000494:pharmacology
chemical_list: D000143:Acids; D001639:Bicarbonates; D002712:Chlorides; D014667:Vasopressins; C019323:deoxycortone pivalate; D003900:Desoxycorticosterone; D000641:Ammonia